The present invention relates to an electric power steering apparatus wherein auxiliary steering power is derived from an electric motor.
2. Discussion of the Prior Art
A typical conventional electric power steering apparatus has a torque sensor for detecting manual torque input to a steering shaft and an electric motor for generating auxiliary steering power so that a load current is supplied to the electric motor in accordance with the level of manual torque detected by means of the torque sensor, thereby assisting the driver with steering force.
The electric power steering apparatus of the type described above is generally arranged to assist the driver with steering force by transmitting the rotation of the electric motor after the speed of the rotation has been reduced through a speed reducing mechanism. The reduction ratio of the speed reducing mechanism cannot be increased unrestrictedly because smooth return of the steering wheel must be ensured. For this reason, the prior art needs a large-sized motor and therefore suffers from the problems of a high rate of consumption of electric current and a need for large torque in a low-speed region where the motor efficiency is low.